4.3BSD-UWisc/lib/learn/eqn/L1.1e

#print
So far all the equations have been centered, which is what
"-ms" does unless you tell it differently.
You can also arrange for equations to be left-adjusted -
that is, right up against the left margin - by saying
  .EQ L
If there is a number, place it _____after the L, separated by a
space, like this:
  .EQ L (3a)

Make the equation in "Example" left-justified with
the number (3.1a) in the right margin and print it
to make sure everything works.  Then type "ready".
#once #create Example
.PP
This is a tiny little text
(which you're undoubtedly sick of by now)
that includes one equation
or at least it will when you find this line:
.EQ
x sup i = y sup i
.EN
and convert it into an equation.
(Naturally I changed it.)
.pl 1
#user
grep '\.EQ  *L  *(3.1a)$' <Example >/dev/null
#log
#next
1.1f 10